1. Field of the Invention
The present invention relates to a heat-assisted magnetic recording head for use in heat-assisted magnetic recording wherein data recording is performed with a recording medium with its coercivity lowered by irradiating the recording medium with near-field light.
2. Description of the Related Art
Recently, magnetic recording devices such as a magnetic disk drive have been improved in recording density, and thin-film magnetic heads and magnetic recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a reproducing head including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a recording head including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider which flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data recording with existing magnetic heads.
To solve the foregoing problems, there has been proposed a method so-called heat-assisted magnetic recording. This method uses a recording medium having high coercivity. When recording data, a magnetic field and heat are simultaneously applied to the area of the recording medium where to record data, so that the area rises in temperature and drops in coercivity for data recording. The area where data is recorded subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization.
In heat-assisted magnetic recording, heat is typically applied to the recording medium by using near-field light. A known method for generating near-field light is to irradiate a plasmon antenna, which is a small piece of metal, with laser light. The plasmon antenna has a near-field light generating part which is a sharp-pointed part for generating near-field light. The laser right applied to the plasmon antenna excites surface plasmons on the plasmon antenna. The surface plasmons propagate to the near-field light generating part of the plasmon antenna, and the near-field light generating part generates near-field light based on the surface plasmons. The near-field light generated by the plasmon antenna exists only within an area smaller than the diffraction limit of light. Irradiating the recording medium with this near-field light makes it possible to heat only a small area of the recording medium.
In conventional heat-assisted magnetic recording heads, the near-field light generating part is often disposed on the leading side with respect to a magnetic pole. An example of such heat-assisted magnetic recording heads is disclosed in JP 2007-257753 A. The leading side with respect to a reference position refers to a side closer to the air inflow end of the slider than is the reference position, and it is typically the side closer to the bottom surface of the substrate on which the reproducing head and the recording head are stacked, than is the reference position.
The heat-assisted magnetic recording head disclosed in JP 2007-257753 A is configured so that laser light emitted from a light source located outside the slider is guided to the plasmon antenna through an optical waveguide that is arranged to extend in a direction perpendicular to the medium facing surface.
The heat-assisted magnetic recording head of such configuration has the disadvantage that the optical path from the light source to the plasmon antenna is long and therefore the light suffers great loss of energy in the path.
JP 2005-4901 A discloses a heat-assisted magnetic recording head in which a light irradiation part (plasmon antenna) is provided on the trailing side with respect to the magnetic pole. The trailing side with respect to a reference position refers to a side closer to the air outflow end of the slider than is the reference position, and it is typically the side farther from the top surface of the substrate than is the reference position. According to the heat-assisted magnetic recording head described in JP 2005-4901 A, it is possible to guide light from a light source to the light irradiation part through a short path by disposing the light source on the trailing side with respect to the light irradiation part.
In the conventional heat-assisted magnetic recording heads, the plasmon antenna is directly irradiated with laser light so that the plasmon antenna converts the laser light into near-field light. This technique has the disadvantage that the use efficiency of the laser light is poor since the laser light can be reflected off the surface of the plasmon antenna or can be converted into thermal energy and absorbed into the plasmon antenna.
Conventional plasmon antennas are small in volume because their sizes are smaller than the wavelength of light. The conventional plasmon antennas therefore show a great increase in temperature when absorbing the thermal energy, which results in the problem that the plasmon antenna expands and protrudes from the medium facing surface to damage the recording medium.